1. The Field of the Invention
The present invention is directed to the field of thermocyclers used in the practice of the polymerase chain reaction (PCR).
2. The Relevant Technology
A number of industrial, technology and research applications utilize thermal cycling to manage applications such as chemical or biochemical reactions or analytical applications.
One important tool in the field of molecular biology which utilizes thermal cycling is the process known as “polymerase chain reaction” (PCR). PCR generates large quantities of genetic material from small samples of the genetic material. This is important because small samples of genetic material may be difficult or expensive to measure or analyze or use for any practical purpose, whereas the ability to produce large amounts of desired genetic material through the PCR amplification process allows one to engage in important actions such as the identification of particular genetic material in a sample, or the measurement of how much genetic material was present, or generation of enough genetic material for use to serve as a component of further applications.
The PCR process is performed in a small reaction vial containing components for DNA duplication: the DNA to be duplicated, the four nucleotides which are assembled to form DNA, two different types of synthetic DNA called “primers” (one for each of the complementary strands of DNA), and an enzyme called DNA polymerase.
DNA is double stranded. The PCR process begins by separating the two strands of DNA into individual complementary strands, a step which is referred to as “denaturation.” This is typically accomplished by heating the PCR reaction mixture to a temperature of about 94 to 96 degrees centigrade for a period of time between a few seconds to over a minute in duration.
Once the DNA is separated into single strands, the mixture is cooled to about 45 to about 60 degrees centigrade (typically chosen to be about 5 degrees below the primer melting temperature) in order to allow a primer to bind to each of the corresponding single strands of DNA in the mixture. This step is typically called “annealing.” The annealing step typically takes anywhere from a few seconds up to a few minutes.
Next, the reaction vessel is heated to about 72 to 73 degrees centigrade, a temperature at which DNA polymerase in the reaction mixture acts to build a second strand of DNA onto the single strand by adding nucleic acids onto the primer so as to form a double stranded DNA that is identical to that of the original strand of DNA. This step is generally called “extension.” The extension step generally takes from a few seconds to a couple minutes to complete.
This series of three steps, also sometimes referred to as “stages”, define one “cycle.” Completion of a PCR cycle results in doubling the amount of DNA in the reaction vial. Repeating a cycle results in another doubling of the amount of DNA in the reaction vial. Typically, the process is repeated many times, e.g. 10 to 40 times, resulting in a large number of identical pieces of DNA. Performing 20 cycles results in more than a million copies of the original DNA sample. Performing 30 cycles results in more than a billion copies of the original DNA sample. A “thermocycler” is used to automate the process of moving the reaction vessel between the desired temperatures for the desired period of time.
It can take about three hours to run about 30 cycles when using conventional equipment. This amount of time is required because of the time that is spent accomplishing a change of temperature between each PCR step, as well as the time required at each target temperature.